> Teacher are covered by QI just as much as cops, and there is much less past precedent on use of force by teachers.

Are they? I think it's hard to answer that question precisely, since qualified immunity is not a law that has been passed but a collection of judicial interpretations. Wikipedia says that it applies to 'government officials', and, even if one takes Wikipedia as definitive, it's not clear to me that that should apply to schoolteachers. The only real way to test whether qualified immunity applies to teachers would be to have it be used in a court case. Has it been?